1. Field of the Disclosure
The disclosure is generally related to ink compositions containing an emulsion and, more particularly, to ink compositions containing an emulsified colorant and/or an emulsified lubricating agent, and writing instruments containing same.
2. Brief Description of Related Technology
Many writing instruments can generally be categorized as either ball pens or markers. Ball pens can often be further characterized, for example, as roller ball pens, gel pens, or ball point pens. Markers can often also be further characterized, for example, as permanent markers, highlighters, dry erase markers, washable markers, and/or other special purpose markers (e.g., metallic markers, correction markers, and other special purpose markers).
A significant problem for ball point pens involves a lack of writing smoothness. A variety of solutions have been implemented to address this deficiency including but not limited to (1) lowering the viscosity of the ink composition, for example, by using various polymer resins and solvent combinations to regulate/reduce its elasticity and/or viscosity, (2) adding miscible lubricants to the ink composition, (3) adding shear-thinning additives capable of demonstrating thixotropic effects to the ink composition, and/or (4) increasing the size of the ball, particularly, in combination with reducing the ink composition viscosity. However, writing smoothness remains an issue for many ball pens.
A significant problem for markers containing pigmented ink compositions involves pigment settling. Pigment settling can occur both when the ink composition is stored in bulk and when it is in an ink delivery system (such as a capillary reservoir system). Pigment settling in an ink delivery system can be particularly problematic for a consumer because it can result in the delivery of an ink composition that does not contain a sufficient and/or intended amount of colorant. To counteract pigment settling, dispersing agents, resins, and additives such as viscosity modifiers have been added to both water- and solvent-based inks so as to stabilize pigment dispersions therein. However, success in eliminating pigment settling has been limited. Consequently, many markers containing pigmented ink compositions should be positioned/orientated in a tip-down fashion otherwise the color intensity of the ink will deleteriously change during the writing life of the markers.